When I was a kid, you could get away with a thin chain and a cheap padlock, that you could open by bashing against the bike stand, and cable locks with cast white metal(probably a zinc alloy) bodies, although the cables used to be a lot thicker back then. Mind you, I had a few locks stolen off my bike at school, but no-one stole my bike! About 20 years later, kids around here would be snapping the bicycle stands off to steal a bike if they couldn't break the locks.
Awww, Thank you so much for the Detailed Reply and lots of suggestions and tips too (y) Wish Bike Theives wouldn't exist, hark back to the old days, when people left their back doors open and could leave their bikes unattended w.o being stolen...
Kryptonite had an exchange programme for their tubular keyed d-locks years ago, masterlock and Oxford Magnum (I think) also changed their design after the issue was publicised on the net, a few years after it was reported on TV. Apparently thieves favoured using a cigarette lighter to soften the pen. Video of someone opening one here:- I'd look for a lock that is either thatcham approved or Sold Secure Gold rated (or maybe silver rated if the bike is insured and the policy approves silver rated locks). Cable locks are pretty hopeless as a main lock, but may be ok as a secondary lock for securing the front wheel. Onguard have some relatively cheap gold rated d-locks, such as their pitbull and thicker heavier Brute lock (which should be more resistant to bolt cropping) in various sizes:- https://www.amazon.co.uk/Onguard-Pitbull-8005-Bike-Cable/dp/B00XAM0NYI I gather their mounting brackets aren't very good. Not very light though, but I doubt you'll get a lightweight lock that is very secure. I own a Kryptonite New York as I got it cheap end of line, due to a change in the mounting bracket design, even heavier and probably a bit better quality, and usually expensive. Be sure to oil the keyhole and to put some mineral oil in the shackle holes and give the key a few turns to thoroughly oil the lock bolts, as the locking mechanisms on hardened steel d-locks are all prone to rusting if not well oiled.
Really?! I'm thinking of buying a D Lock, any ideas of a good, Lightweight type that's isn't too costly! My bikes 2nd hand, but still prone to theft of course!
Those tubular keyed locks on the D-lock can be opened with a rolled up bit of cardboard, or the case of a bic pen if is fits. You clone the key by pressing the carboard/plastic tube into the lock.